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Journal of Bacteriology, September 1998, p. 4676-4685, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Analysis of the Exochelin Locus in Mycobacterium smegmatis: Biosynthesis Genes Have Homology with Genes of the Peptide Synthetase Family

Shengwei Yu, Ellen Fiss, and William R. Jacobs Jr.*

Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York 10461

Received 7 April 1998/Accepted 29 June 1998

Mycobacteria secrete the siderophore exochelin when grown under iron-limiting conditions. In order to understand iron uptake mechanisms in mycobacteria, we have taken a genetic approach to identify those genes involved in exochelin biosynthesis and transport in Mycobacterium smegmatis. Of the 6,000 chemically mutagenized clones of M. smegmatis mc2155 screened on agar plates containing chrome azural S, 19 mutants that had lost the ability to produce or secrete exochelin were identified. Thirteen of these mutants were complemented by a single M. smegmatis cosmid. Sequence analysis of this cosmid revealed nine open reading frames, three of which are homologous to genes encoding transporter proteins, which are likely involved in exochelin transport. Complementation and Tn10 mutagenesis analysis identified two new genes, fxbB and fxbC, which are required for exochelin biosynthesis. The fxbB and fxbC genes encode large proteins of 257 and 497 kDa, respectively, which are highly homologous to peptide synthetases, indicating that exochelin biosynthesis occurs by a nonribosomal mechanism.

* Corresponding author. Mailing address: Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461. Phone: (718) 430-2888. Fax: (718) 518-0366. E-mail: jacobs{at}aecom.yu.edu.

Journal of Bacteriology, September 1998, p. 4676-4685, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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